New breakthrough could make concrete stronger, greener & cheaper

New research by Rice University scientists promises a stronger, greener and more durable alternative to the ubiquitous Portland cement used to make concrete.

The scientists have developed micron-sized calcium silicate spheres that can be prompted to self-assemble into solids that are stronger, harder, more elastic and more durable than cement.

Rice materials scientist Rouzbeh Shahsavari and graduate student Sung Hoon Hwang view the spheres as building blocks that can be made at low cost and promise to mitigate the energy-intensive techniques now used to make cement, the most common binder in concrete.

The spheres were formed in a solution around nanoscale seeds of a common detergent-like surfactant.

Shahsavari, an assistant professor of materials science and nanoengineering at Rice University, observes that cement particles are amorphous and disorganised, making them vulnerable to cracks. With the new material, they can channel polymers or other materials in between the spheres to control the structure from bottom to top and predict more accurately how it could fracture.

He added that the spheres were also suitable for bone-tissue engineering, insulation, ceramic and composite applications as well as cement.

The latest research is inspired by how nature coordinates interfaces between dissimilar materials, particularly in nacre (mother of pearl), the material of seashells. Nacre's strength comes from alternating stiff inorganic and soft organic platelets.

The researchers discovered they could control the size of the spheres that range from 100 to 500 nanometres in diameter by manipulating surfactants, solutions, concentrations and temperatures during manufacture.

According to Shahsavari, the size and shape of particles in general have a significant effect on the mechanical properties and durability of bulk materials like concrete. Elaborating on the advantages of the spheres, he said one can mix spheres with different diameters to fill the gaps between the self-assembled structures, leading to higher packing densities and thus mechanical and durability properties.

When the strength of cement is increased, manufacturers can use less concrete, decreasing the weight as well as the energy required to make it in addition to the carbon emissions associated with cement manufacture.

Since spheres pack more efficiently than the ragged particles found in common cement, the resulting material will be more resistant to damaging ions from water and other contaminants and should require less maintenance and less-frequent replacement, he added.